1. Field of the Invention
The present invention relates to a pneumatic, e.g. pressurized air operated, control system for shifting the auxiliary section of a compound transmission. In particular, the present invention relates to an improved pneumatic control and interlock system for range type compound transmission.
2. Description of the Prior Art
Compound transmissions of the range or combined range/splitter type are well known in the prior art as may be seen by reference to U.S. Pat. Nos. 3,105,395; 3,138,965; 3,171,300; 3,283,613 and 4,754,665, the disclosures of which are hereby incorporated by reference.
Briefly, such transmissions typically comprise a multiple speed main transmission section connected in series with a range type auxiliary section wherein the range step is greater than the total ratio coverage of the main transmission section.
In such transmissions, the main section is typically shifted by means of a shift bar housing assembly controlled by a manually operated shift lever or the like and the auxiliary range section is shifted by means of button or switch, usually manually operated, which controls a remote slave valve/actuator mechanism. As the range section often utilizes synchronized jaw clutches, to provide acceptable shift quality and prevent undue wear and/or damage to the range section synchronized jaw clutches, a range shift should be initiated and completed while the main transmission section is in neutral.
In view of the above, the prior art compound range type transmissions usually include a control systems, usually a pneumatic control system, including interlock devices, which allowed a range shift to be preselected by use of a selector button or switch at a master control valve but not initiated until the main transmission section is shifted to, or at least towards, the neutral condition. Such systems typically utilized interlocks of the mechanical type on the range section actuator mechanical linkage which physically prevented movement of the range section shift fork until the main section shifted into neutral or of the type wherein the valve supplying pressurized air to the range section piston is either disabled or not provided with pressurized fluid until a shift to main section neutral is sensed or is only activated and provided with pressurized fluid while the main section is shifted to and remains in neutral. Examples of such transmissions and the control systems therefor may be seen by reference to U.S. Pat. Nos. 2,654,268; 3,138,965 and 4,060,005, the disclosures of which are hereby incorporated by reference.
The prior art devices were not totally satisfactory as excessive stress was applied to the mechanical interlock/linkages, sever range section shifting could occur and/or the main transmission section could be re-engaged prior to completion of the range section shift which would result in damage to the range section synchronizers (especially during an upshift) or in stranding the range section in a disengaged condition.